Automated inspection systems that utilize imaging technology are frequently used to verify whether an object meets desired quality parameters and/or to measure process variability, provide process control and perform other tasks. Such systems are frequently used to perform vision-based inspection of products such as textile webs and machined parts and in industrial production environments, such as food processing and parts manufacturing.
Automated inspection systems frequently utilize a machine vision system having an imaging device, at least one illumination or light source and associated image processing equipment. An important factor in machine vision applications is the quality of illumination, as illumination plays a critical role in the appearance of patterns. Further, illumination quality takes on increased importance when the measurement process relies on specific illumination characteristics. Examples of specialized illumination characteristics are bright field, coaxial, backlight, telecentric and dark field illumination.
An exemplary setup 10 depicting light source and imaging device geometry for providing dark field illumination of a V-shaped defect 12 located on a surface 14 is shown in FIG. 1. An imaging device 16 such as a camera is located above the defect 12 at three-dimensional 3D spatial location C(x1, y1, z1). A light source 18 is located offset from an axis 20 of the imaging device 16 at 3D spatial location L(x2, y2, z2) and is oriented at an angle of illumination or incident angle α relative to the surface 14. The light source 18 generates sufficient light to illuminate a first portion 22 of the defect 12 to form a bright region 24 whereas a second portion 26 of the defect 12 is not illuminated to form a dark or shadow region 28 in particular, the bright 24 and shadow 28 regions are in a field of view 30 of the imaging device 16. Further, light 32 that impinges on flat surfaces (i.e. surfaces that do not include a defect 12) is reflected out of the field of view 30 of the imaging device 16.